The principal means of passive fire protection in structures is by completely enclosing areas with fire barriers. Fire barriers may include fire doors, walls, ceilings, and floors. Fire barriers play an integral role in managing a fire by interrupting the spread of smoke, other toxic gases, and the fire itself from one fire zone into another. Often, the potentially weakest points in a fire barrier are the doors to an area, both because the doors may not be as fire retardant as the walls and ceilings of an enclosure, and also because there generally are cracks under and around the doors through which smoke and toxic gases may pass during a fire.
Fire doors generally are specifically constructed to retard the progress of fires in at least two ways. First, the doors are constructed of fire resistant materials such as steel, fiberglass, certain types of particle board, or diatomaceous earth, among others. Second, fire doors may include one or more regions of intumescent material that expands when heated, minimizing or eliminating cracks in and around the door.
A number of standard tests of fire door effectiveness have been developed for use in the building industry. These are published, for example, in the Uniform Building Code (UBC), the International Building Code (IBC), and by the National Fire Protection Association (NFPA), Underwriter's Laboratories (UL), and the American Society for Testing and Materials (ASTM), among others. Various agencies test fire doors using these standard tests, and assign ratings to fire doors that indicate their effectiveness at slowing the progress of a fire. Door testing agencies include Intertek Testing Services (USA), Underwriter's Laboratories (USA), Omega Point Laboratories (USA), Chiltern International Fire, Ltd. (UK), and Warrington Fire Research (UK), among others. Ratings of fire doors are generally provided in minutes, and typically vary from 45 minutes to 120 minutes.
Disclosures of fire doors are found in U.S. Pat. Nos. 6,115,976 and 6.643,991. The disclosures of each of these documents are incorporated herein by reference. The advantages of the fire door and fire door components provided in this disclosure will be understood more readily after considering the drawings and the detailed description of the preferred examples.